International Research Journal of Geology and Mining (IRJGM) (2276-6618) Vol. 4(3) pp. 84-100, April, 2014
DOI: http:/dx.doi.org/10.14303/irjgm.2013.028
Available online http://www.interesjournals.org/IRJGM
Copyright©2014 International Research Journals
Review
Deformation history of Nugrus- Sikiat Belt, South
Eastern Desert, Egypt; implication for Tectonic
Environment
*1, 2
Ibrahim WS, 2Mostafa MS, 2Ibrahim ME, 1Watanabe K and 3Soliman FA
1
Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan
2
Nuclear Materials Authority, Cairo, Egypt
3
Suez of Canal University, Ismailia, Egypt
*Corresponding Author Email: W-Ibrahim@mine.kyushu-u.ac.jp
Abstract
The Nugrus –Sikait belt comprises metamorphic exposures which are mainly represented by two
nappes; upper nappe (dismembered ophiolitic rocks) and lower nappe (pelitic, para-amphibolite and
cataclastics assemblages) separated by ophiolitic mélange. Intra-cratonic association (granitic and
gabbroic rocks) intrudes these rock associations. Styles, overprinting relationships between the
different structural fabrics, where each rock assemblages show its own tectonic print revealed that
Nugrus-Sikait belt underwent five distinct episodes of deformation (from D1to D5). Compression event
(D1) with NW-SE to NNW-SSE σ1 trend. E-W thrust faulting and forming E-W isoclinal folds (Df1).
Compression event (D2) with NE-SW to ENE-WSW σ1 trend. NW-SE thrust faulting and forming NW-SE
folding (Df2). Transpressonal sinistral shearing (D3) with NW-SE to NNW-SSEσ1
σ1 trend including top-toNW oblique-slip shearing and NNE-SSW dextral strike-slip shearing led to development of the NugrusSikait ductile shear zone and formed NNW-SSE folding (Df3). This event associated with emplacement
of granitic intrusions, which cause folding around horizontal N-S direction (Df4). Extensional event (D4)
with NE-SW to ENE-WSW σ3 trend deformation probably related to exhumation of the complex with
NNW-SSE normal and strike-slip faulting. Extensional event (D5) with NNW-SSE to N-S σ3 trend
restricted to the alkali feldspar granite. ENE-WSW to E-W normal faulting, this event associated with
emplacement of post granitic dikes and veins. The tectonic evolution of the NSB can place important
insights into a proposed tectonic model suggesting a back-arc basin tectonic environment. The basin
was formed as faulted bounded basin controlled mainly by E-W and N-S trending.
Keywords: Tectonics, Structures, Paleostress field, Folding, Nugrus-Sikait.
INTRODUCTION
The Nugrus –Sikait belt (NSB), located within W. El Gemal
environs, and represents the southeastern continuation of
Wadi Hafafit Culmination (WHC). The WHC as well as
NSB attracted the attention of many authors among
themHashad and Hassan (1959),Basta and Zaki
(1961),Hassan (1964 and 1973), Hashad et al. (1972), El
Shazly and Hassan (1972), Bugrov et al. (1973), Sabet et
al. (1976), Stern (1981), El Gaby (1983), El Bayoumi
(1984), El Gaby et al.(1984), Hegazy (1984), Stern and
Hedge, (1985), EI-Gaby et al.(1988), Hilmy et al.(1990),
Takla et al. (1992), Al Filali et al. (1993), El Ramly et al.
(1993), Saleh (1998), Assaf et al. (2000), Ibrahim et al.
(2000), Fowler and El Kalioubi (2002), Ibrahim et al.
(2004), Rashed (2006) and Ibrahim et al. (2007a, bandc).
The NSB is structurally located between the southern and
central Eastern Desert domains (Figure 1), where the
low-angle thrust zone, Nugrus Thrust, represent a zone
of discontinuity between the two domains of the Eastern
Desert (Stern and Hedge, 1985). This thrust fault
localizes the limit between the medium metamorphic
grade associations and the low metamorphic grade
ophiolitic melange assemblage at the study area.
The studied area is a Precambrian basement terrain
constituted of different lithological assemblage of igneous
and metamorphic rocks. Most of these rocks are highly
deformed which is featured by the frequent presence of
Ibrahim et al. 85
Figure 1.Generalized geological map of the Eastern Desert of Egypt
showing the distribution of the basement rocks and the location of
NSA with respect to the limits between the basement subdivisions,
Southern Eastern Desert (SED), Central Eastern Desert (CED) and
Northern Eastern Desert (NED) (from Stern and Hedge, 1985)
multiple mesoscopic structures.
On the other hand, Nugrus-Sikaitbelt is very rich in
various economic mineralization (U, Th, Nb, Ta, Zn, Be,
Sn, Cu, Ga and REEs). That makes this area as one of
the most important and promising mineral resources
areas in the Eastern Desert of Egypt.
The relation between igneous, metamorphic rocks as
well as shear zones is important as a mean of
determining the history of the deformational events of the
study area that make up an orogenic system and
configure its structural pattern. In particular, measuring
the structural fabric pattern of geologic bodies in the field
studies can help to establish the link between magma
emplacement and tectonics.
This paper attempts to characterize, deduce, analyze and
reconstruct the tectonic setting that controlling the
structure pattern of the Precambrian crystalline rocks
throughout NSB using the ductile and brittle deformation
analysis techniques.
Geological Setting
Based on the detailed field studies, the lithological
associations found in NSB comprise two nappes; upper
nappe (ophiolitic rocks) and lower nappe (pelitic, paraamphibolite and cataclastics assemblages) separated by
ophiolitic mélange. These rock associations are latterly
86 Int. Res. J. Geo. Min.
Figure 2.Detailed geologic map of Nugrus-Sikait Belt (NSB), showing
the regional structural lines, the main wadis as well as the investigated
sites distribution among the different rock types
intruded by granitic and gabbroic rocks (Figure 2).These
rocks show gradual variation from low grade schist facies
at the upstream of W. Nugrus (epidote and chlorite
facies), thorough the medium grade amphibolite facies
(W. Abu Rusheid and downstream of W. Nugrus) to high
grade amphibolite facies in tectonic mélange along W.
Sikait (staurolite– kyanite–sillimanite facies).
The NS Brock associations are cut by various dykes
and veins that comprise various lamprophyre dykes
except the last two phases of granites (muscovite and
alkali feldspar granites) which are mostly cut by various
quartz and pegmatitic veins. The litho-stratigraphic rock
types are summarized on Table (1).
The contact between the first two rock assemblages is
a structural contact represented by a regional NW-SE
trending thrust belt dipping due NE direction whereas the
intrusion of the granitoid pulses are controlled mainly by
the NW-SE, NE-SW and N-S to NNW-SSE structural
trends. In addition to that, some of these structural trends
were associated with or responsible for the encountered
folding in NSB that exhibits asymmetric varied
geometries and axial plane orientations including buckle,
chevron, sheath and kinking folds. In terms of interlimb
angle they range between open to isoclines, and in terms
of axial plane orientation they include gently inclined to
almost recumbent folds whereas the interference patterns
were recorded in some exposures.
Deformation Analyses
NSBwas the object of intensive detailed systematic
analyses of the structural fabrics e.g. foliation, lineation,
folds, fault populations, joints, sense of movement and
shear criteria, etc. The field measurements (more than
14,000 measurements) were collected throughout
109sites distributed in almost all the outcropping rock
types in NSB (Figure 2).For each site, attention was paid
to chronological criteria, overprinting relations, cross-cut
relationships between fault and fracture systems.
The superposition of different movement marks
slickenside lineation on a single fault plane, the
reactivation of the pre-existing fault planes due to later on
stress fields as well as fault geometry with respect to
foliation planes and folding (fault-fold relationships) in
order to differentiate and then categorize the succession
Ibrahim et al. 87
Table 1.Compiled litho-stratigraphic rock types of NSB
Rock types
Post granitic dikes and veins
Intrusive rocks
Alkali feldspar granites
Composition and Description
Various types of
dykes(lamprophyre and
hornblendite) and veins
(pegmatite andquartz)cut through
the study area
Highly weathered granites
composed of quartz, K-feldspar,
plagioclase andcuts through the
muscovite granite
Geologic Setting
Lamprophyre dikes cut all the rock
units at NSB except the muscovite
and alkali feldspar granites which
are mostly cut by quartz and
pegmatite veins.
Occurrences
Dikes and veins are distributed
among all the rock units at NSB
The emplacement of granitic
plutons in the study area is
controlled by two basic structural
trends (NW-SE and E-W). To the
south the pluton is surrounded by
layered meta gabbros thrusted over
ophiolitic mélange.
The right upstream side of both
W. Sikait and W. Abu Rusheid
intruding along the contact
between the ophiolitic mélange
and the biotite monzogranites
and as offshoots along W.Nugrus
Occurs as white small masses
along W. Sikeit, W. Nugrus and
north of W. Abu Rusheid and as
emplacing dike-like bodies
injected into the biotite monzo
granites
Represent 70% of granitic rocks
in the study area. Exposed to the
north east of W. Abu Rusheid
and upstream of W. Sikait
Muscovite monzo granites
Composed of quartz, K-feldspar,
plagioclase and muscovite,
commonly contain xenoliths of
mafic rocks and abundant garnet
crystals
biotite monzogranites
Composed mainly of quartz,
plagioclase, feldspars, and
biotite.
Younger Gabbros
Coarse-grained gabbroid rocks
comprise olivine gabbro and
hornblende gabbro with
gradational contacts
The emplacement of gabbroid rocks
elongate through the same NW-SE
structural trend
Cover a total area about 4 km2,
to the NW of NSB
Cataclastics
Include protomylonites,
mylonites, ultra mylonites and
silicified ultra mylonites
(quartzite) with gradational
contacts.
Highly foliated, the intercalations
between the proto mylonite and
mylonite rocks are common
manifesting the sedimentary
origin.The ophiolitic mélange are
thrusted over the cataclastic rocks.
Exposed at eastern side of W.
Abu Rusheid covering about
3km 2and at eastern side of W.
Sikait as small area (0.5km2)
forming low land terrain.
para-amphibolites
These rocks are fine- to mediumgrained and shows greenish grey
to deep green color and composed
mainly of hornblende, plagioclase
and biotite
Display well defined foliation with
relics of primary bedding.
Lower nappe
metapelites
Ophiolitic mélange.
Composed mainly of Biotite schist
and hornblende schist.
Display relics of primary bedding,
foliations, and laminations, minor
and macro-folding and are
intruded by biotite granite and
muscovite granites.
Exposed only at the eastern side
of W. Abu Rusheid covering a
small area.
Cover the downstream of W.
Sikait on the two sides.
NW-SE Thrust contact
Composed mainly of Mélange
matrix (mainly schists) that
encloses abundant fragments of
meta-periodotite, metapyroxenite and orthoamphibolites of variable sizes
and dimensions. The matrixesare
represented by wide varieties (talc
schist, quartzo-feldspathic schist,
garnet-mica schist, tourmalinegarnetiferous-biotite schist,
graphite schist and sillimanite
schist).
The schists are the result of regional
metamorphism of pelitic and
psammo-pelitic sediments. These
rocks are highly foliated and
featured by the frequent presence
of folds, boudinaged quartz and
pegmatite lenses extending
parallel to the foliation planes.
E-Wand NW-SE Thrust contacts
Biotite schists are forming the
greatest part of the schists in the
study area and the main rock unit
of Gabal Sikait, Talc schist is
located to the east of W. Sikait,
Tremolite-actinolite schists located
near the contact with granitic rocks
at W. Abu Rushied with related
beryl occurrences, Garnetiferous
hornblende-biotite schists on
eastern side of W. Sikait and
middle of W. Abu Rushied and
Graphite schists as thin bands at
middle and end of W. Sikait
88 Int. Res. J. Geo. Min.
Metagabbros
Upper nappe (dismember ophiolite)
Table 1.Continuation
Metaprediotites
Exhibit a wide variation in colors,
varying from dark grey to dark
green in color. These rocks are
characterizes by well-developed
layering which reflect varying in
composition in mafic and light
minerals. The ophiolitic
metagabbros are observes in
sheeted mass overlying the
ophiolitic mélange
The metagabbros are tholeiitic,
high alumina, high–Ti ophiolite
and equivalent to oceanic gabbros
and back–arc basin
Light brown color, soft, compact,
soapy with the development of
foliation in some places. Metaperidotites are mostly highly
serpentinized and in many
places transformed into talccarbonates, cream-color rocks.
Characterized by tholeiitic, high–Ti
ophiolite, equivalent to
metamorphic peridotites and
ultramafic cumulate of low
temperature Alpine type.
Represent the most predominant
rock unites within the studied
area where they are covering the
eastern and southern parts of the
study area.
E-W Thrust contact
W.Nugrus, W.Sikait and W.Abu
Rushied
Figure 3.Chronological criteria; example of relative chronology used in dating the
tectonic events in NSB.1st F1 fold system developed in metagabbroic bands with
E-W trending fold axis, 2nd F2 isoclinals folds with NW-SE running fold axes, 3rd
right lateral displacement along NNW-SSE strike-slip fault system and 4thENEWSW dip-slip normal fault system
of the deformational events.
The analysis of these structural elements allowed the
determination of both local and then regional orientations
of the principal paleo-stress axes and establishing some
relative chronologies (Figure 3). The results have been
synthesized in order to reconstruct a schematic timing of
the paleo-stress field evolutions that in turns allow
defining the tectonic and geodynamic evolution.
Ductile deformation analyses
The different rocks behave differently under stress; some
rocks when subjected to the same stress will be fractured
or faulted while others will be folded or recrystallized and
foliated
during
deformation
and/or
dynamic
metamorphism. The higher in temperature (i.e. the
deeper within the crust), the more likely that ductile
Ibrahim et al. 89
Figure 4.Foliation data representations as rose diagrams (1= strike,
2=dip direction, 3= dip angle and 4=lower hemisphere stereographic
projection, NSB. (a. metagabbros, b. mélange - metasediments and
c. cataclastics)
mechanism dominates over brittle mechanisms in
controlling the style of deformation. Folding, mineral
lineation and foliation in the metamorphic exposure rocks
in Nugrus –Sikait belt are the most remarkable ductile
deformational fabrics.
Detail studies of the ductile deformational fabrics was
carried out among17 sites distributed along the
metagabbros, mélange, metasediments and cataclasics
exposures, where foliations, folding and refolding are well
developed. More than 2,000measurements of foliation,
lineaments and fold axes have been collected so that 587
measurements in metagabbros, 1,072 measurements in
mélange and metasediments and 420 measurements in
cataclastics.
These
measurements
have
been
categorized and analyzed according to their trend
distribution in each lithological type. Each system of
foliation has been analyzed to deduce its principal
compression direction with the help of the stereographic
projection software packages GEOrient version 9.4 and
Tector, Angelier (1989, 1990 and 1994).
1) Foliations
The metagabbro sets of foliations are arranged according
to E-W and NW-SE main striking trends, suggesting N-S
and NE-SW trending compression (Figure 4a).The
mélange and metasediments sets of foliations are
arranged due to ENE-WSW and NW-SE directions,
reflecting NNW-SSE and NE-SW compressional trends
(Figure 4b).The cataclastics set of foliations are oriented
due to NW-SE to NNW-SSE general trend, revealing a
compressional trend around the NE-SW direction (Figure
4c). Accordingly, it is believed that the NE-SW
compression trend is post to and/or associated with
cataclastics, whereas the N-S compression is the oldest
one and restricted to metagabbros and or mélange.
2) Folding
At NSB, folding are restricted to the foliated layered
90 Int. Res. J. Geo. Min.
Figure 5.Density-contoured lower hemisphere Schmidt net stereograms of structural data, sites; S19, S18 and A29 Shading
for all stereograms are from lowest to highest concentration representing poles to foliation measurements (a, b and c) for the
E-W folding. Remark the impact of NW-SE folding then NNW-SSE folding (b)
metagabbros, mélange, metasediments and cataclastic
rocks and are generally localized around and/or
associated with the thrust belt sheet around W. Nugrus
and W. Sikait, where the 17 sites of fold measurements are
located (Figure 2).
These folds exhibit varied geometries including
buckle, chevron, sheath and kinking folds with interlimb
angle ranging from 30o to 120o reflecting open to tight fold
types which are agreement with Marshak and Mitra
(1988). In additional to that, the axial plane inclinations
are found to be ranging widely from 0o to 90o at Nugrus –
Sikait belt, where upright, overturned and recumbent folds
were recorded. Generally, the folds as well as foliation
measurement analyses categorized four sets of folding
which fold axes trended E-W, NNW-SSE, NNE-SSW and
NW-SE with minor N-S ones (Figures 5, 6 and 7). Later
on, these fold sets have been dislocated by an intense
strike slip deformational regime (Figure 3).
a) E-W Folding
The E-W set of folding is characterized by cylindrical
geometry, where the fold axes are plunging gently in E
and W and run in E-W direction (Figure 5). The impact of
the later fold sets is shown in Figures 5 and 6, where the
interference fold pattern has been clearly recorded
(Figure 6). This set of folding reflects an axis of shorting
oriented around the N-S direction. In many sites, as
shown in Figure (6), the E-W fold set has been refolded
either during the NW-SE phase of folding and/or the
NNW-SSE one (Figure 5; b).
Accordingly, E-W set of folds was considered as the
oldest phase of folding (Df1) in NSB and represent an
initial phase of shortening with an axis oriented around
the N-S direction.
b) NW-SE Folding
Folds of NW-SE oriented fold axes (Figure 7) are widely
recorded in the study area. Generally, this set was
developed as asymmetric folds ranging from normal
upright to overturned with different styles and geometries
(Figures 6 and 7).
The detailed field observations recorded the
association between this set of folds and the NW-SE
thrust fault system, i.e. it is related to the same event of
deformation (Figure 8). The interpretations of the shape
of the folded rock types and their internal structure as
well as the relative field chronological data suggest a
second phase of folding (Df2) defined by NW-SE oriented
fold axes (Figure 6).
c) NNW-SSE Folding
Folds of NNW-SSE oriented fold axes (Figure 9) are
widely recorded as intrafolial event developed due to
either coaxial strain or shear folded line strain forming
discrete as well as zonal crenulations and kinking.
Generally, this set has asymmetric geometry as tight to
isoclinal folds, with axial planes approximately parallel to
the plane of the foliation, and hinges lying at a small
angle to the local extension lineation. These folds are
well developed, especially in the meta-gabbro and
mélange.
The folds of this set have been regarded either around
or associated with a right lateral oblique slip dislocation
system of regional scale that parallel to and/or at small
angle with the NW-SE running thrusts(Figure 10c).
Moreover, the relative field chronological fold-fold
relationship between the NNW-SSE set of folds and
either the E-W or the NW-SE ones reveals that both E-W
Ibrahim et al. 91
Figure 6.Fold interference pattern showing the impact of NW-SE folding;
(a), E-W then NW-SE folding. (b), NW-SE thrusts and/or strike-slip faults
on the E-W and NW-SE sets of folds. Remark the impact of these
sequences of folds shown on the density-contoured lower hemisphere
Schmidt net stereograms of structural data, sites; S19 and S24
or the NW-SE sets of folding are earlier to that of the
NNW-SSE orientation (Figures 6b and 10a,b), and
suggest a third phase of folding (Df3) defined by NNWSSE oriented fold axes.
horizontal fold axes oriented around the N-S direction
that could be due to the response, accommodation and
reorientation of the preexisting structural fabrics to the
stresses created during the emplacement of the granitic
intrusion.
d) Folding around N-S
Brittle deformation analyses
Folds of fold axes oriented around N-S direction are
rarely recorded in the study area. This set has been
recorded with almost horizontal axes (Figure 11)
especially near granite contacts with mélange. The shape
of the folded rock types and their internal structure
suggest a fourth phase of folding (Df4) defined by
In the present study, two quantitative approaches were
followed. The first depends on field characterization of
the conjugate fault system; neoformed or inherited, as
well as recording of the relative chronology and their
associated features (intra-formational breccias, slumps,
92 Int. Res. J. Geo. Min.
Figure 7.Density-contoured lower hemisphere Schmidt net stereograms of structural data from the
NSB. Shading for all stereograms are from lowest to highestconcentrations representing poles to
foliation measurements reflecting the NW-SE folding; sites A13, N14, S17,S18 and S24. Remark the
impact of N-Sfolding (F4), (a) on NW-SE ones
Figure 8.Example illustrating the contemporaneous relation between the NW-SE
trending axes set of folds and the NW-SE thrust fault system recorded at Abu
Rushied area. Remark the parallelism of the fold axis and the bearing of the NW-SE
thrust fault system, where the fold axes could be plotted within the NW-SE thrust
fault plane, in the same time, the fold axes delineates clearly the plane of the NW-SE
thrust fault system
ect.) that give a very good and direct indication about the
tectonic regime from the chronological point of view. The
second approach is based on the quantitative numerical
analysis and treatment of the fault-slip data using the
Ibrahim et al. 93
Figure 9.Density-contoured lower hemisphere Schmidt net stereograms of structural data from the NSA.
Shading for all stereograms are from lowest to highest concentration representing poles to foliation
measurements (a, b and c) for the NNW-SSE folding; sites A17 and S14
Figure 10.Fold interference pattern showing the impact of NNW-SSE folding (F3), (a, b, and c). Remark the
zonal kinking (a) as well as, intrafolial NNW-SSE oriented folds axes, folded vein in foliated meta-gabbro
with axial planes parallel to the foliation (d)
inversion method, of fault slip data, to compute the
paleostress tensor Angelier (1989, 1990 and 1994).
More than 109 sites have been studied in detailed
(Figure 2). These sites are distributed almost in all the
rock types cropping out in the area so that, 24 sites in
metagabbro, 39 sites in mélange, 11 sites in cataclastics,
27sites in monzogranite, 7 sites in muscovite granite and
7sites in alkali feldspar granite. Each site contains
several tens of tectonic features measured in small area.
It is defined by the coherence and the abundance of fault
populations and by the quality of the outcrop.
The quantitative analyses of 8,927 fault slip data sets
revealed that more than 539 paleostress tensors (Figures
12-15) such , 51 paleostress tensors are characterizing
pure compressional regime, 305strike-slip regime and
183forextensional regime. The calculated tensors
characterize, according to their nature, the paleostress
regimes and the orientation of the mean stress axes, i.e.
94 Int. Res. J. Geo. Min.
Figure 11.Example of the recorded folds with almost horizontal fold axes oriented around
the N-S direction, NSB
Figure 12.Distribution of measurement sites in metagabbro, where the
geometrical distribution (in roses) for fault strikes and paleostress tensors
measured in metagabbro rock unit. (1)= all fault trends rose, (2) = inverse
(thrust) fault analyses, (3) =strike-slip fault analyses and (4) = normal fault
analyses. (a)=compression (σ1) trends, (b) =strike slip system (σ1 and σ3) and (c)
=extension (σ3) as well as examples of the calculated paleostress tensors for
some key sites (A35, N1, N2, N3, N16, N18, S5 and S12)
Ibrahim et al. 95
the directions of extension (σ3) and/or that of
compression (σ1). The quantitative analyses of brittle
deformations enable us to reconstruct the paleostress
field evolution that reflects the regional deformation
mechanisms. The calculated paleostress tensors
presented in terms of rock types.
oriented (σ3). In addition to that, these NW-SE thrust
faults show the trace of recent reactivation as oblique slip
normal faults (site S11, Figure 13) during an extensional
phase of deformation dominated by N-S oriented (σ3).
c. Cataclastic paleostress systems
a. Metagabbro paleostress systems
The analysis of approximately 2,145 fault slip data
(275inverse (thrust), 1,046 strike-slip and824 normal)
measured in 24 sites throughout the metagabbro
revealed 122 paleostress tensors, so that 21 of them
correspond to thrust or inverse fault systems, 56
paleostress tensors correspond to strike-slip fault
systems and 45 paleostress tensors correspond to
normal fault systems (Figure. 12).
The pure compression of thrust fault systems are
mainly oriented due to NW-SE and ENE-WSW to E-W
(Figure 12, a) whereas, the extensional paleostress
tensors are oriented around N-S direction with ENEWSW to E-W minor trends (Figure 12, c), and the strikeslip fault systems revealed multi-trend pattern (Figure 12,
b).
The NW-SE fault systems were recorded at the
contacts between the metagabbros and the down
thrusted mélange, meta-sediment and cataclastics where
the metagabbro is thrusted over them. The field
chronological criteria defined later reactivation of the NWSE trending thrust fault as strike-slip dominated by ENEWSW trending σ1and N-S trending σ3(site A35)(Figure
12).
b. Mélange-meta-sediment paleostress systems
The analysis of approximately 2,735 fault slip data (280
thrust, 1,529 strike-slips and 926 normal) measured in 38
sites throughout the mélange-metasediment rocks enable
the calculation of 178 paleostress tensors, so that 24 of
them correspond to thrust fault systems, 96paleostress
tensors correspond to strike-slip fault systems and 58
paleostress tensors correspond to normal fault systems
(Figure 13).
The pure compression are mainly oriented due to
NNW-SSE, NW-SE and ENE-WSW to E-W (Figure13, a)
whereas, the extensional paleostress tensors are
oriented around N-S direction with NE-SW and ENEWSW minor trends (Figure 13, c). The strike-slip tensors
show multidirectional trends for both (σ1) and(σ3) that
could be related to cycles of strike-slip regimes during
which almost all the preexisting fault systems have been
reactivated as strike-slip ones(Figure 13, b). The
geometrical analyses of the thrust fault systems show
that the E-W (sites N15 and S17, Figure.13). Moreover,
the NW-SE thrust fault systems have been reactivated as
strike-slip dominated by NW-SE oriented (σ1) and NE-SW
The
cataclastic
exposures
enable
recording
approximately 848 fault-slip data (55 thrust, 407strikeslipsand386 normal) measured in 11 sites. About 55
paleostress tensors have been calculated, so that 6
correspond to thrust faults, 27 correspond to strike-slip
faults and 22 correspond to normal faults (Figure 14).
The main compression(σ1) oriented due to NE-SW to
ENE-WSW (Figure 14, a), whereas the strike-slip tensors
define WNW-ESE and NW-SE directed (σ1) associated
with orientations around N-S and NE-SW for
(σ3)(Figure14, b).The extensional paleostress tensors(σ3)
show permutation around NNW-SSE and ENE-WSW
directions with minor NE-SW (Figure 14, c).
The strike-slip system of both (σ1 −NW) and (σ3 −NE)
commonly observed as transpressional sinistral shearing,
including top-to-NW oblique-slip shearing with NNE-SSW
dextral strike-slip shearing which led to development of
the Nugrus-Sikait ductile shear zones. The geometrical
analyses of NW-SE to NNW-SSE thrust fault systems
reflect a later reactivation in strike-slip regime dominated
by NW-SE oriented (σ1) and NE-SW oriented (σ3)(sites
A21, Figure14). In addition to that, the N-Sand E-W
normal fault systems (sites A21and A22, Figure14) are
lithologically sealed and show tilted geometry restricted
only to metasediment-cataclastic reflecting an earlier
extensional event dated to the meta-sediment-cataclastic
and prior to folding.
d. Paleostress systems in granitic rocks
According to detailed field observations, strike-slip and
normal faults are the commonly observed fault patterns in
the three types of granitic rocks, outcropping at NSB. The
approximately 3199 fault slip data (2266 strike-slip and
933 normal) measured in 41 sites throughout the granitic
rocks were analyzed (Figure 15).
The biotite monzogranite measurement sites (27)
provide 2,114 (446 strike-slip and 175 normal) enable the
calculation of 121 paleostress tensors, such89 tensors
correspond to strike-slip fault systems and 32 tensors
correspond to normal fault systems (Figure 15).
The strike-slip tensors are dominated by NE-SW, E-W
and NW-SE oriented (σ1) respectively associated with
NW-SE, NNE-SSW and NE-SW oriented (σ3), while the
extensional tensors define N-S and NNE-SSW to NE-SW
oriented (σ3) (Figure15). The geometrical analyses of the
E-W and N-S normal faults (sites A34, N13 and S31,
Figure15) reflect later reactivation as oblique slip during
NE-SW acting extension (σ3).
96 Int. Res. J. Geo. Min.
Figure 13.Distribution of measurement sites in mélange-metasediments, where the geometrical
distribution (in roses) for fault strikes and paleostress tensors. (1)= all fault trends rose, (2) = inverse
(thrust) fault analyses, (3) =strike-slip fault analyses and (4) = normal fault analyses. (a)=compression (σ1)
trends, (b) =strike slip system (σ1 and σ3) and (c)=extension(σ3) as well as examples of the calculated
paleostress tensors for some key sites(A10, A16, A20, N4, N15, S11, S14, S21 and S29)
The muscovite monzogranite (446 strike-slip and 175
normal faults) as well as the alkali feldspar granite (352
strike-slip and 112 normal faults) fault slip data analysis
reveal 37 tensors corresponding to strike-slip faults with
almost the same pattern as that obtained from the
monzogranite (Figure 15).Moreover, the paleostress
tensors corresponding to normal faults (26 tensors) show
a clear N-S trending (σ3) restricted to the alkali feldspar
granite.
DISCUSSION AND CONCLUSION
Several contributions have been made to the deformation
and structural setting of this area,Garson and Krs (1976)
considered that Wadi Shait thrust lies within the range of
the regional N45º-60ºE block faulting and should be older
than the Wadi Nugrus thrust, which lies within the range
of deep seated tectonic zones N 30º-35º W. Abdel Khalek
and Abdel Wahed (1984) suggest three deformational
Ibrahim et al. 97
Figure 14.Distribution of measurement sites in cataclastics, where the geometrical distribution (in
roses) for fault strikes and paleostress tensors. (1)= all fault trends rose, (2) = inverse (thrust) fault
analyses, (3) =strike-slip fault analyses and (4) = normal fault analyses. (a)=compression (σ1)
trends, (b) =strike slip system (σ1 and σ3) and (c)=extension(σ3) as well as examples of the
calculated paleostress tensors for some key sites(A20, A21, A22,A24, A29, N11 and S25)
phases;d1, d2 and d3. The first deformational phase (d1)
is represented by NW-SE axial planes and axes plunging
SE and NW respectively. The second (d2) is represented
by tight overturned and have SW plunging axes. The third
deformational phase (d3) is the weakest in intensity and
resulted in open and tight symmetric and asymmetric
folds and have NW-SE axial planes. Assaf et al. (2000)
stated that the Nugrus –Sikait area involved in
superimposed folding events. The F1 folds resulted in
isoclined folding and other primary structures around
WNW-ESE axes. The F2 folds refolded the F1 folds into
upright to overturned and even recumbent folds about
NW-SE axes. The F3 folds are of mild intensity compared
to the F1 and F2 generations due to NNE-SSW trend.
According to observations in the NSB, the thrust and
strike-slip type of faulting that are recorded in
metagabbro, ophiolitic mélange and meta-sediments
seem to be fold accommodation faults show geometric
and kinematics relationship to surrounding folds. In
particular, their strikes are generally parallel to the strike
of fold axes and they show more or less symmetric
arrangement to the axial planes of folds. Moreover, fold
structures below and above the thrust plane are almost
similar; fold axes can be connected from footwall into the
98 Int. Res. J. Geo. Min.
Figure 15.Distribution of measurement sites indifferent granitic rocks (biotite
monzogranite, muscovite monzogranite and alkali feldspar granite), where the
geometrical distribution (in roses) paleostress tensors. (a)=strike slip system (σ1 and σ3)
and (b) =extension (σ3) as well as examples of the calculated paleostress tensors for
some key sites (A1, A2, A6, A11, A14, A34, N5, N13, N20, S8, S10, S20, S27 and S31
hanging wall block and they may terminate out-offoliation, i.e. thrust tips form an angle with foliation and do
not necessarily run into foliation planes as well as the
development of folds with sinistral asymmetry in dextral
shear zones.
The fold analyses showed in NSB: an initial planar
fabric with E-W trending stretching D1 was folded around
older E-W trending Df1 axes then around NW-SE
trending Df2 axes followed by regional NE-SW shortening
associated with normal upright to overturned folding
around NNW-SSE trending Df3 axes. Finally, a fourth
phase of folding (Df4) defined by horizontal fold axes
oriented around the N-S direction that could be due to the
response, accommodation and reorientation of the
preexisting structural fabrics to the stresses created
during the emplacement of granitic intrusion.
Deformation analysis includes; the paleostress studies
(brittle) as well as foliation and fold analyses (ductile)
allow proposing a reconstruction of a consistent scheme
of tectonic development for the NSB. These analyses
indicate that the NSB underwent five distinct episodes of
deformation (D1-D5).Summarizing, the major tectonic
regimes as follows, from oldest to youngest.
(1)- Pure compression event (D1) with NW-SE to NNWSSE σ1 trend. E-W thrust faulting and forming E-W
isoclinal folds (Df1) restricted to meta-gabbros and/or
mélange only.
(2)- Pure compression event (D2) with NE-SW to ENEWSW σ1 trend. NW-SE thrust faulting and forming NWSE folding (Df2) recorded in meta-gabbros, mélange and
cataclastics.D1 and D2 are found to be coherent with
prograde metamorphism.
Ibrahim et al. 99
.
(3)-Transpressonal sinistral shearing (D3) with NW-SE to
NNW-SSEσ1 trend including top-to-NW oblique-slip
shearing and NNE-SSW dextral strike-slip shearing led to
development of the Nugrus-Sikait ductile shear zone and
formed NNW-SSE folding (Df3).This event associated
with emplacement of granitic intrusions (at leastbiotite
and muscovite monzogranite) which cause folding around
horizontal N-S direction (Df4).
(4)-Extensional event (D4) with NE-SW to ENEWSWσ3 trend deformation probably related to
exhumation of the complex and is characterized by NNWSSE normal faulting and strike-slip within extensional
context.
(5)- Extensional event (D5) with NNW-SSE to N-S σ3
trend restricted to the alkali feldspar granite. ENE-WSW
to E-W normal faulting, this event associated with
emplacement of post granitic dikes and veins.
The tectonic evolution of the NSB can place important
insights into a proposed tectonic model suggesting a
back-arc basin tectonic environment. The basin was
formed as faulted bounded basin controlled mainly by EW and N-S trending then the western bloc underwent
northeastward-directed rollover, thrusting over and
shearing with the western margin of the eastern bloc
followed by stress release and faulting within extensional
context associated with granitic intrusions. Finally, the
prevailing of extension tectonics associated with the initial
opening of the Red Sea.
ACKNOWLEDGEMENTS
This study was supported by Egyptian Nuclear Materials
Authority (fieldwork), and Japan MEXT program (PhD
scholarship to the first author). We are grateful to all
members of Abu Rushied project in Nuclear Materials
Authority for they assistance in the fieldwork.
REFERENCES
Abdel Khalek ML, Abdel Wahed M (1984). Structural setting of Hafafit
gneisses, Eastern Desert, Egypt, Abstracts of papers presented at
the 5th International Conference of Basement Tectonics, Cairo,
Egypt, pp. 8
Angelier J (1989). From orientation to magnitudes in paleostress
determination using fault slip data. J. Struct. Geol. 11:37– 50
Angelier J (1990). Inversion of field data in fault tectonics to obtain the
regional stress: III. A new rapid direct inversion method by analytical
means. Geophys. J. Int. 103:363– 376.
Angelier J (1994). Faults slip analysis and palaeostress reconstruction.
In: Hancock, P.L. Continental Deformation. Pergamon, Tarrytown,
NY, 4:53– 100
Assaf HS, Ibrahim ME, Zalata AA, El- Metwally AA, Saleh GM (2000).
Polyphase folding in Nugrus-Sikeit area south Eastern Desert, Egypt.
JKAW: Earth Sci., 12:1-16.
Basta EZ, Zaki M (1961). Geology and mineralization of Wadi Sikait
area, south Eastrn Desert, J. geol. U. A. R., 5(1):1-38
El Bayoumi RMA (1984). Ophiolites and mélange complex of Wadi
Ghadir, Eastern Desert, Egypt. Bull. Fac. Earth Sci., King Abdul Aziz
Univ., Jeddah, 6:324-329
El Gaby S (1983). Architecture of the Egyptian basement complex.
th
5 Int.Conf. On Basement tectonics, Egypt
El Gaby S, El-Nady OM, Khudeir AA (1984). Tectonic evolution of the
basement complex in the CED of Egypt. Geol., Rundsch 73:10191036
El Gaby S, List FK, Tehrani R (1988). Geology, evolution and
metallogenesis of the Pan-African belt in Egypt. In: S. El Gaby and R.
O. Greiling (eds), The Pan-African Belt of northeast African and
adjacent areas, Fried. Vieweg and Shon, Braun Schweig,
Wiesbaden, pp. 17-68
El Ramly MF, Akaad MK (1960). The basement complex in the central
Eastern Desert of Egypt between latitudes 24° 30 and 25° 4^N Geol.
Surv. Egypt, paper 8:35.
El Ramly MF, Greilling RO, Kroner A, Rashwan AA (1984). On the
tectonic evolution of the Wadi Hafafit area and environs.
EastertDesert of Egypt. Fac. Earth Sci.. king AbdulazizUniv., Jeddah,
Saudia Arabia, Bull. 6:113-126.
El Ramly MF, Greilling RO, Kröner A, Rashwan AA, Rasmy H (1993).
Explanatory note to accompany the Geological and Structural maps
of Wadi Hafafit area. Eastern Desert of Egypt. Geological Survey of
Egypt. Paper 68:53.
El Shazly EM, Hassan MA (1972). Geology and radioactive
mineralization at Wadi Sikait-Wadi El-Gemal area. South Eastern
Desert, Egypt. J. Geol. 16(2):201
El-Filali IA, Hassan MA, Hashad AH (1993). Significance of some
mantled gneiss domes in the Arabian- Nubian shield. Ann, Geo.
Surv., Egypt. V(XIX):33 – 46.
Fowler A, El Kalioubi B (2002). The Migif-Hafa.t gneissic complex of the
EgyptianEasternDesert: fold interference patterns involving multiply
deformed sheath folds. Tectonophysics 346:247–275.
Garson MS, Krs M (1976). Geophysical and geological evidence of the
relationship of Red Sea traverse tectonic to ancient fractures, Geol.
Soc. Am. Bull., 87: 169-181.
Hashad AH, Hassan MA (1959). Report on the prospection work carried
out in Wadi El Gemal area, south Eastern Desert, Egypt. Internal
Report, AEE, Cairo, UAR.
Hashad AH, Hassan NA (1979). On the validity of an ensimatic island
arc cratonization model to the evolution of the Egyptian shield, Ann.
Geol. Surv., Egypt, IX : 70 –90.
Hashad AH, Sayyah TA, El-Kholy SB, Youseff A (1972). Rb – Sr
isotopic age determination of some basement Egyptian granites,
Egypt. J. Geol. V(16):269-281
Hassan MA (1964). Geology and petrographical studies of the
radioactive minerals and rocks in Wadi Sikait- Wadi El Gemal area.
EasternDesert, U. A. R: M. Sc thesis faculty of science, CairoUniv.
Pp. 165
Hassan MA (1973). Geology and geochemistry of radioactive columbitebearing psammitic gneiss of Wadi Abu Rusheid. South Eastern
Desert, Egypt: Annals of Geol. Surv. Egypt. V(III):207-225
Hegazy HM (1984). Geology of Wadi El Gemal area. Eastern Desert,
Egypt. Ph. D. Thesis, Assiut Univ., Egypt. Pp. 271
Hilmy ME, El Bayoumi RM, Eid AS (1990). Geology geochemistry, and
mineralization of the Psammitic gneiss of Wadi Abu Rushied, Eastern
Desert, Egypt. J. Afr. Earth Sci., v (11): 197-205.
Ibrahim ME, Abd El-Wahed AA, Rashed MA, Khaleal FM1, Mansour
GM, Watanabe K (2007a). Comparative study between alkaline and
calc-alkaline lamprophyres, Abu Rusheid area, south Eastern Desert,
th
Egypt. The 10 Inter. Min., Petrol., and Metall. Eng. Conf., Assuit
univ., pp. 99-115
Ibrahim ME, Amer TE, Saleh GM (1999). New occurrence of some
nuclear materials and gold mineralization at Wadi Sikait area, south
Eastern Desert, Egypt. First seminar on Nuclear Raw Materials and
their technology, Cairo, Egypt, pp. 271-284
Ibrahim ME, Assaf HS, Saleh GM (2000). Geochemical alteration and
spectrometric analyses in Abu Rusheid altered uraniferous gneissose
granites, South Eastern Desert, Egypt Chem. Erde 60:173-188.
Ibrahim ME, Saleh G, Rashed M, Watanabe K, Motomura Y (2006).
Epithermal Base metal mineralization in Lamprophyre, south Eastern
Desert, Egypt. El Emarat Conf. Geol., Abst., pp. 211.
Ibrahim ME, Saleh GM, Hassan MA, El Tookhi, Rashed MA (2007).
Geochemistry of lamprophyres bearing uranium mineralization, Abu
th
Rusheid area, south Eastern Desert, Egypt. The 10 Inter. Min.,
100 Int. Res. J. Geo. Min.
petrol., Metall. Engin, Conf., AssuitUniv.
Ibrahim ME, Saleh GM, Hassan MA, El-Tokhi MM, Rashed MA (2007b).
Geochemistry of lamprophyres bearing uranium mineralization, Abu
th
Rusheid area, south Eastern Desert, Egypt. The 10 Inter. Min.,
Petrol., and Metall. Eng. Conf., Assuit univ., pp. 41-55
Ibrahim ME, Saleh GM, Ibrahim IH, Azab MS, Khamies AA, Oraby F,
Abu El-Hassan EA Ragab AA (2004). Geologic and ground
spectrometric prospecting of the Abu Rusheid-Sikeit shear zones,
th
South Eastern Desert, Egypt. 7 Arab Conference on the Peaceful
Uses of Atomic Energy, Sanaa,Yemen.
Marshak S, Mitra G (1988). Basic methods of structural geology.
Prentice Hall Inc., New Jersey, pp. 446
Rashed MA (2005). Geologic studies on a new occurrnce of nuclear
materials in Abu Rusheid area, South Eastern Desert, Egypt. Ph. D.
Thesis, MansouraUniv. (Demitta), pp. 139
Sabet AH, Tsogoev VB, Bordonosov VP, Shoblovsky RG, Kossa M
(1976). On the geologic structures, laws of localization and prospects
of Abu Rushied rare metals deposit Annals. Geol. Surv. Egypt. V
(VI):181-197
Saleh GM (1997). The potentiality of uranium occurrences in Wadi
Nugrus area, south Eastern Desert, Egypt. Ph. D. Thesis Mans. Univ.
pp. 171
Stern RJ (1981). Petrogenesis and tectonic setting of late Precambrian
ensimatic volcanic rocks, Central Eastern Desert of Egypt.
Precambrian Research, 16: 195-230.
How to cite this article: Ibrahim WS, Mostafa MS, Ibrahim ME,
Watanabe K and Soliman FA (2014). Deformation history of
Nugrus- Sikiat Belt, South Eastern Desert, Egypt; implication
for Tectonic Environment. Int. Res. J. Geo. Min. 4(3): 84-100